Conventionally, valve timing control devices have been known that control a relative rotational phase between a driving-side rotational member rotating synchronously with a crankshaft in an internal combustion engine and a driven-side rotational member rotating synchronously with a camshaft for opening and closing a valve, and keep an excellent running state of the internal combustion engine at every number of revolutions. In a valve timing control device, a fluid pressure chamber formed by the driving-side rotational member and the driven-side rotational member is partitioned into a retard chamber and an advance chamber by a partitioning portion provided in the driven-side rotational member. The relative rotational phase between the driving-side rotational member and the driven-side rotational member is controlled by supplying and discharging a working fluid to and from the retard chamber and the advance chamber.
This valve timing control device includes a lock mechanism capable of locking the relative rotational phase between the driving-side rotational member and the driven-side rotational member at a predetermined phase. As a result of locking the relative rotational phase, an optimum valve opening/closing timing can be achieved when the internal combustion engine is started, and generation of collision noise caused by swinging of the partitioning portion is suppressed.
An exemplary lock mechanism includes a lock hole in one of the driving-side rotational member and the driven-side rotational member, and includes a lock member and a coil spring for applying a biasing force to the lock member in the other of the driving-side rotational member and the driven-side rotational member. With this lock mechanism, a locked state is achieved by inserting the lock member in the lock hole by means of the biasing force, and an unlocked state is achieved by retracting the lock member from the lock hole by means of the pressure of the working fluid that is larger than the biasing force.
PTL 1 discloses a valve timing adjustment device capable of reducing a linking force generated when the locking pin is operating so as to be fitted to a fitting hole. A linking force refers to a force generated when two objects in contact with each other with a fluid therebetween are about to move apart from each other, in directions opposite to the directions in which the objects move away from each other, due to an increase in the volume of the fluid between the contact surfaces and a reduction in the pressure in the gap therebetween.
An end of the locking pin on the side opposite to the fitting hole side is usually a flat surface, and the flat surface at the end of the locking pin comes into surface contact with a front plate when in an unlocked state. At this time, the working fluid leaking from the advance chamber or the retard chamber is present as a fluid film between the end of the locking pin and the front plate. If the locking pin in this state begins to move in the fitting direction as a result of a locking operation, in some cases, the linking force is generated due to this fluid film, in the direction opposite to the direction of the biasing force of the coil spring exerted on the locking pin.
If the linking force is large, an initial operation of the locking pin delays, and the locking pin is not fitted to the fitting hole in some cases. As a result, there is a possibility that the relative rotational phase between the driving-side rotational member and the driven-side rotational member cannot be locked at the predetermined phase, and the internal combustion engine cannot be started. In order to reduce the linking force, it is effective to reduce the area of the fluid film, and prevent a decrease in the pressure with an expansion of a gap between the end of the locking pin and the front plate as a result of the working fluid actively entering the gap when the locking pin moves in the fitting direction.
The valve timing adjustment device in PTL 1 is configured such that the end surface of the locking pin on the side opposite to the fitting hole is tapered and comes into line contact with the front plate. Since the end surface of the locking pin and the front plate are in line contact, the area of the fluid film is reduced. Furthermore, a space between the end surface of the locking pin and the front plate at portions other than the portion in line contact is filled with the working fluid. When the locking pin begins to move in the fitting direction and the gap expands, the working fluid around the gap enters the gap and prevents the reduction in the pressure in the gap. As a result, the linking force at the time when the locking pin begins to move in the fitting direction is reduced.